1. Field of the Invention
The present invention relates to an ophthalmic apparatus which comprises an alignment detecting system, such as a non-contact tonometer, a keratometer or a corneal endothelium photographing apparatus.
More particularly, the present invention relates to an ophthalmic apparatus which projects an index light beam from an oblique direction onto the cornea of the eye to be examined, receives the light beam reflected on the cornea with a photoelectric element, and measures positional relation between the eye and the apparatus with respect to the Z-direction (forward and backward direction) based on the output of the photoelectric element.
2. Description of the Related Art
In the aforementioned known apparatus, an error is introduced into the result of Z-alignment measurement, if dislocation with respect to the XY direction (rightward/leftward, upward/downward) exists.
In order to solve the problem, an ophthalmic apparatus proposed in JP-A No. Hei 7-23907 has an error correcting system for correcting the result of Z-alignment measurement based on an XY alignment dislocation of a main unit from a correct position.
However, the ophthalmic apparatus described in JP-A No. Hei 7-23907 needs to store the measured XY-alignment dislocation, and calculate an accurate Z-alignment dislocation based on the stored XY-alignment dislocation. Accordingly, it takes considerable time to output an accurate Z-alignrent dislocation data.
If so-called flick movement occurs, the eye moves while calculating an accurate Z-alignment dislocation, so that it is difficult to accomplish the alignment.